1. Field of the Invention
The disclosure relates to a method and apparatus for printing substantially uniform organic films over target print areas and having profiled edges. More specifically, the disclosure relates to novel method and apparatus for printing an organic film (interchangeably, layer) by providing vaporized material, distributing the vaporized material over a target area and condensing the vaporized material to form a substantially uniform film on the target area.
2. Description of Related Art
The manufacture of organic light emitting devices (OLEDs) requires depositing one or more organic films on a substrate and coupling the top and bottom of the film stack to electrodes. The film thickness is a prime consideration. The total layer stack thickness is about 100 nm and each layer is optimally deposited uniformly with an accuracy of better than +/−2%. Film purity is also important. Conventional devices form the film stack using one of two methods: (1) thermal evaporation of organic material in a relative vacuum environment and subsequent condensation of the organic vapor on the substrate; or, (2) dissolution of organic material into a solvent, coating the substrate with the resulting solution, and subsequent removal of the solvent.
Another consideration in depositing the organic thin films of an OLED is placing the films precisely at the desired location. There are two conventional technologies for performing this task, depending on the method of film deposition. For thermal evaporation, shadow masking is used to form OLED films of a desired configuration. Shadow masking techniques require placing a well-defined physical mask over a region of the substrate followed by depositing the film over the entire substrate area. Once deposition is complete, the shadow mask is removed. The regions exposed through the mask define the pattern of material deposited on the substrate. This process is inefficient, as the entire substrate must be coated, even though only the regions exposed through the shadow mask require a film. Furthermore, the shadow mask becomes increasingly coated with each use, and must eventually be discarded or cleaned. Finally, the use of shadow masks over large areas is made difficult by the need to use very thin masks (to achieve small feature sizes) that make said masks structurally unstable. However, the vapor deposition technique yields OLED films with high uniformity and purity and adequate thickness control.
For solvent deposition, ink jet printing can be used to deposit patterns of OLED films. Ink jet printing requires dissolving organic material into a solvent that yields a printable ink. Furthermore, ink jet printing is conventionally limited to the use of one or two layer OLED film stacks, which typically have lower performance as compared to four for five layer film stacks used in vapor deposited devices. The stack limitation arises because printing typically causes destructive dissolution of any underlying organic layers. Consequently, one must engineer each layer such that it is undamaged by the wet deposition of each subsequent layer, and this greatly constrains the material and stack options. Finally, unless the substrate is first prepared with defined regions that contain the ink within the areas where the films are to be deposited, a step that increases the cost and complexity of the process, ink jet printing has very poor thickness uniformity as compared to vapor deposited films. The material quality is also typically lower, due to structural changes in the material that occur during the drying process and due to material impurities present in the ink. However, the ink jet printing technique is capable of providing patterns of OLED films over very large areas with good material efficiency.
No conventional technique combines the large area patterning capabilities of ink jet printing with the high uniformity, purity, and thickness control achieved with vapor deposition for organic thin films. Because ink jet processed OLED devices continue to have inadequate quality for widespread commercialization, and thermal evaporation remains too expensive and impractical for scaling to large areas, it is a major technological challenge for the OLED industry to develop a technique that can offer both high film quality and cost-effective large area scalability.
Finally, manufacturing OLED displays may also require the patterned deposition of thin films of metals, inorganic semiconductors, and/or inorganic insulators. Conventionally, vapor deposition and/or sputtering have been used to deposit these layers. Patterning is accomplished using prior substrate preparation (e.g., patterned coating with an insulator), shadow masking as described above, and when a fresh substrate or protective layers are employed, conventional photolithography. Each of these approaches is inefficient as compared to the direct deposition of the desired pattern, either because it wastes material or requires additional processing steps. Thus, there is a need for these materials as well for a method and apparatus for depositing high-quality, cost effective, large area scalable films.